1. Field of the Invention
The present invention relates to a motor apparatus including a Lundell motor having a Lundell-type rotor.
2. Description of Related Art
Lundell-type rotors are widely used for vehicle alternators required to be capable of adjusting power generation voltage thereof by controlling a field current. The Lundell-type rotors have a structure including a rotor core constituted by a cylindrical boss section and a plurality of claw-poles which extend from both axial end surfaces of the boss section radially outward at a predetermined circumferential pitch, and then extend in the axial direction such that the claw-poles extending from one of the end surfaces alternate with the opposed claw-poles extending from the other end surface, and also including a field coil wound around the boss section.
There is also known a magnet-equipped Lundell-type rotor in which each claw-pole is provided with permanent magnets at both its circumferential sides in order to strengthen the field flux thereof. For example, Japanese patent Application Laid-open No. 2007-329989 describes a vehicle alternator including such a magnet-equipped Lundell-type rotor invented by the same inventor as named in the present application.
Also, Japanese patent Application Laid-open No. 2005-130656 and Japanese patent Application Laid-open No. 2005-192345 describe a vehicle-mounted motor or a vehicle alternator including such a magnet-equipped Lundell-type rotor.
It is also known to utilize a reluctance torque due to the difference between a d-axis inductance Ld and a q-axis inductance Lq for performing torque adjustment in a conventional IPM motor (Interior Permanent Magnet motor) or a SYRM (Synchronous Reluctance Motor) having a rotor core with the projecting magnetic pole characteristic.
Generally, vehicle-mounted motors are required to be torque adjustable over a wide rotation range. However, the above conventional IPM motor has a problem in that its efficiency is low in a high speed range, because a field-weakening control has to be performed in the high speed range. Also, the SYRM has problems in that its output torque is small for its body size because the SYRM uses only the reluctance torque, and its efficiency is low because of the necessity to generate the d-axis flux.
While on the other hand, the foregoing motor including a Lundell-type rotor can be used as an excellent torque-adjustable motor for a vehicle, because its field torque Tf (=field flux Φf×q-axis current Iq) can be adjusted by controlling its field current If irrespective of the rotational speed thereof.
However, the motor including a Lundell-type rotor has a problem in that its torque cannot be changed rapidly, because of the large inductance of its field coil. In addition, the motor including a Lundell-type rotor has further problems in that the body size per output torque is large compared to the IPM motor, and its efficiency is low because of the necessity to pass a field current to the field coil.